Virus infections (i.e, for example, influenza A and B viruses) are responsible for yearly epidemics in both children and adults. Illnesses caused by influenza A and B viruses are clinically indistinguishable and may cocirculate Van Voris et al., “Influenza viruses” p. 267-297. In: R. B. Belshe (ed.), Textbook Of Human Virology. PSG Publishing Co., Littleton, Mass. (1984). Antiviral chemoprophylaxis and therapy is currently very limited (i.e., for example, influenza A virus-specific agents amantadine and rimantadine). Rapid detection of influenza virus is therefore essential to facilitate patient management and to initiate effective control measures.
Presently known procedures for preparing a specimen for Direct Fluorescence Antibody (DFA) staining are expensive, laborious and time consuming. Usually, a drop of a cell suspension from the specimen is dried on a glass slide and fixed with a precipitating or denaturing fixative such as acetone, methanol and ethanol. These compounds act to reduce the solubility of protein molecules and by disrupt protein tertiary hydrophobic interactions. After fixation, the samples are stained with fluorescent antibodies involving several steps: i) labelling; ii) washing; and iii) adhering a coverslip. Finally, the samples are examined under a fluorescence microscope.
Further problems in DFA techniques are encountered during the microscopic examination because the antibody preparations commonly contain a general protein counter stain, such as Evans Blue, to help in identifying cells. This counter stain also stains non-cellular material which can make identifying cells difficult. Further, if the cells are not completely dry, they can be lost during the processing steps, leading to an inadequate number of cells to make a judgment as to the presence of the virus. Current DFA methods also require a highly skilled technician to prepare, read and interpret results because of the non-specific staining mucus or debris that can be found in the specimen. Cell morphology and staining patterns are also compromised when the cells are dried onto the glass.
What is needed in the art is an improved DFA assay with better accuracy and faster processing time than those currently available.